Electric measuring apparatus



Feb. 5, 1929. 1,701,358

]c. CAMILLI ETAL ELECTRIC MEASURING APPARATUS Filed Dec. 8. 1926 Fi .2. FTQBQ.

Inventors: Guglielmo Ccrmifli, Ara-m Bogqjiom, bLJ

Then- Attorneg.

a rent and voltage the quantity is relatively small as for example in the measurement of Patented Feb. 5, 1929.

UNITED STATES PIAFTENVJTYFOFFICE;

GUe IEnMo CAMILLI AND ABAM BoYaJI AN, or mammnAssAcHUsE'rTs, AS-

7 srenoes T0 GENERAL ELECTRIC COMPANYLA oonroRATIoNfoF NEW YORK.

ELECTRIC MEASURING AFPARATUS. 7

Application fi led December a, 1826. Serial Im 153,428.

apparatus'for measuring the power of al- I ternating current circuits and is' particularly beneficial for measuring these quantities when due to the-phase relation between curpower at very low power factors.

'lheordinary wattmeter isjnot su table for the accurate measurement of power at very low power factors. More sensitive measuring apparatus than the ordinary wattmeter has been provided for this purpose but in general such apparatus is delicate, complicated and expensive. It is the object of our invention to provide accurate, rugged and relatively inexpensive apparatus for the purpose under consideration.

In carrying our invention into effect we prefer-to employ two wattmeters; One of these wattmeters is employed to obtainv a measuring current for the second wattmeter of such magnitude and phase angle that. the desired measurement may be made under ideal conditions by the second wattmeteiag The features of ourinvention which are believed to be'nov'el and patentable will be pointed out in-the'claims appended hereto. For a better understanding of ourinvention reference is made in the following description to the accompanying drawing in e which Fig. 1 shows the'application of our invention where the wattmeter A is used to obv tain a current for the voltage coil of the wattmeter B which is proportional to and in phase with the desired measurin'gcomponent of the voltage; Figs. 2 and 3 are vector diagrams explanatory of the invention as applied in Fig. 1; Fig. 4 is substantially similar to supplies a measuring current to the, current coil rather than to the potential cations of the invention."

Referring 'to F g. 1, let usassume that 1t is desired to measure the power ofa circuitv have an ordinary 5 ampere, 110 volt wattmeter in which the full scale deflection is 500 watts, it is seen that even with the coils energized at full rating the power is only Fig. 1 except. that the wattmeter A coil of wattmeter B; Figs. 5 and 6 show furtherappli-g.

E and I being 7 v 5 X 110 X .0 1:=5 watts. Such a' reading would be practically impossible to observe accurately since it would correspond to about one scale graduation for the ordinary wattmeterQ Aside from this, the accuracy of the ordinary :wattmeter at such low power factors is poor, since the temperature andphase angle errors of the meter are at a maximum. with respect to the power measurement. InFig; 1 the wattmeter A has the usual current coil 10 and volt-agecoil 11 connected in and across the circuit 9 as usual. Likew1se,the wattmeter Bhas the usual current and. voltage coils 12 and 13 respectively.

Wattmeter A has in addition to the usual voltage coil 11 an auxiliary voltage coil 14 of few turns. 'l hesetwo voltage coils may be wound together andconstitute the voltage-winding of] the meter. 'The auxiliary coill i of wattmeter A and the voltage vcoil 13 ofwattmeter B are connected 1n series and sup lied from some source havmg the same frequency and. approximately the same phase angleasthe current in the site to thepower component of coil 11 so that this wattmeter'will read zero. Fig. 2 shows the vector relations of the currents in the coils of wattmeter ,A and Fig. 3 those of wattmeter B. i

In Fig.- 2 10 represents the vector of the current in coil 10, 11 the vector of the current in coil 11. The power component ofvector 11", which is in phase with 10,'is rep-.- resented at 15. The current in coil 14 is adjusted until this wattmeter reads zero and then we know that the power component supplied by coil 14:, which is represented at :14, F1g. 2, isequal and opposite to the power component 15'... Now, the voltagecurrent of .wattmeter B is in phase or substantially in phase with the current in its current coil 12 so thatthis wattmeter is operating at substantially unity power factor; Now if the number of turns in coil 13 is say 100 times the turns in coil 14, wattmeter B will give a large scale deflection which if the meter is accurate will be an accurate measurement of the power of circuit 9 and we may represent the vectors of the ampere-turns of coils 12 supplied to meter B. W'attmeter B is not only operating at substantially unity power 7 factor where the phase angle and temperature errors are a minimum, but it gives 100 times the deflection in the example given that an ordinary wattmeter would give for the same measurement. The zero reading wattmeter A need not have any scale but merely a zero mark. The accuracy of the method depends upon adjusting the current in coil 14: so that this meter reads zero. null method of adjustment easily obtainable to a high degree of accuracy by the proper design 01 the A meter. i

In the remaining figures A and B are used to designate the zero reading and measurement meters respectively. I

In Fig. 4, the voltage coils 16 and 17 of the wattmeters A and B are connected in parallel across the circuit 9. The current coil 18 of meter B is connected in series with. an auxiliary current coil 19 and an adjusting resistance 20 across the circuit 9. The main current coil 21 of meter A supplies the wattless and watt components of the circuit, the latter of which is neutralized by coil 19 so that meter B is supplied by substantially in phase currents proportional to the power 01'' the circuit when meter A is adjusted by means of the resistance 20 to read zero.

Fig. 5 shows an application of the invention where the current coils or" the A and B wattmeters are connected in parallel. In this case wattmeter B is an ordinarytype wattmeter, the current coil 21 of which is wound for smaller current and more turns than usual but for the same ampere turns as usual. For a 1% power factor load this current coil need not carry more than 1% of 5 amperes. If desired to take care of power factors as high as 10% the current coil 21 may be designed for ampere in which case however the deflection for lower power factors would be smaller. Series multiple connections for this winding might also be used for doubling its power factor range. The current coil 21 of wattmeter B is shown as having in series with it a resistance 22, preferably not less than live times the reactance or the coil, the more the better. The purpose of this resistance is primarily to make the impedanceangle of this branch as small as possible. Zero phase angle, that is unity power factor of the impedance, is not necessary and as much a 30 degrees in the phase angle of this branch is permissible without serious error in the readings. Thus no calibration of the resistance 22 is neces- This is a sary. This branch also contains a source of variable voltage obtained by means of the variable transformer device 23, the primary coil 24 of which is excited from the line voltage as are the Voltage coils 25 and 26 of .the two w'attmeters through potential transtormers, if necessary. The purpose of the device 23 to assist in the resolution of the line current into power and reactive components as will be explained presently. The current coil 21'' of the A wattmeter which is connected in parallel with coil 21 in the circuit 9 is intended to carry the bulk of the reactive component of the line current, which means the bull: of the line current for low power factors, and is therefore designed tocarry say 5 amperes and is suitable for use with the usual current transformer. Pret a resistance 28 is connected in shunt to this coil to compensate for the phase angle error of the potential coil 26.

The operation of this modification is as approximately in phase with the line voltage;

When the power component ofthis current is ust equal to that of the line current, it means that the power component is flowing entirely through branch 21 and only the reactive component is flowing through branch 27. VJattmeter A therefore reads zero andthe power is measured b wattmeter B at high 1 I a power .ractor, large deflection and high accuracy be made b h s 111 constant and ad- 'justing the resistance 22.

'Fig. 6 shows the same general schemein which the power and reactive components of the voltage circuit are segregated for the purpose described. In this case the lead cur in series relation but this does not mean that they have the same voltage. The connection shown is to provide a voltage across The proper adjustment might also the potential coil 32 corresponding to the reactive component and a small voltage across coil 31 corresponding to the power component. For low power factor loads the coil 31 needs to be wound for only a small percentage of normal voltage and correspondlarger current. The impedance of coil 31 will be very low as compared to that of coil.

32. The potentialfcoil 31 is shunted b a low adjustable resistance 33 which is pre erably not more than th of the resistance of the coil itself. Coil 31 is also shunted by the secondary of a current transformer 34, the primary of which is connected in the li.ne 9. The operation is as follows Assume that the ratio of current transformer 34 is one to one s across coil 32. The bulk of the current from transformer 34 will flow throughthe res1st--- ance 33 and thus there will be lmpressed across coil 31 a voltage in phase'with the load current. N ow, by varyingthe resistance 33 until meter A reads zero, it will be evident that the voltage drop across coil 31 is such that a current corresponding to thepower component of the line voltage flows through coil 31 and that only the quadrature component flows in coil 32. There may be a small quadrature component across coil 31 also, but it does no harm to any part of the circuit or to the wattmeter readings The derivation of the necessary inphase voltage from the load current'may be obtained in various ways. \VattmeterB thus operates at high, power factor and gives a large deflection of high accuracy. I

In general the A or zeroreading wattmeter of the modifications described above is made sensitive. T hismay be readily accomplished since we are notinterested in a large scale deflection or in a rugged construction. The B wattmeter on the other hand may be'made rugged and have: a large scale deflection. These requirements which are incompatible to obtain in a single meter are by means'of our invention divided between the two meters so that one meter satisfies one set of'requiremerits and the other meter the other set of requirements. The conflict, or the difliculty, i

of obtaining these requirements in a single meter is thus avoided and each meter may be especially designed to fulfill its particular function with a high-degree of accuracy.

In any of the examples given above, the B meter may be replaced by an ammeter and a voltmeter and the power obtained by calculation. Likewise the B meter may be of the integrating type and automatic means provided to maintain the zero reading on the A meter.

In accordance with the provisions of the patent statutes, we have described the prin ciple of operation of our invention, together with the apparatus which we now'consider to represent the best embodiment thereof, but

We desire to have it understood that the apparatus shown and described is onlyillusg out by other means.

What we claim-as new 1. The method of measuring the power of and if desire to se- I cureby'Letters Patentof the United States,

- trative and that the invention may be carried a low power factor alternating current circult sub ect to. varying current and voltage which consists in obtaining a current in' phase wlth and proportional to one of said vana bles, obtaining asecond current substantially 1n phase wlth said variable but proportional is inphase with the first mentioned variable regardless of variations in power factor, and p lnphase'product of saidtwo measuring the currents. V v

2. The method of measuring the power of a low powerfactor alternating-current circuit which consists in obtaining a current in phase with and proportional'to thecircuit current, obtaining a second current substantially in phase withsaid first mentioned cur-' torque producing component of the main excitation of said winding, such that a null reading of the wattmeter is obtained, and a second wattmeter having one of its windings excited by said auxiliary excitation and the other winding excited by that variable of the circuit which is in phase therewith. j 1

4. Apparatus for measuring the power of low power factor circuits comprising. a 'zero reading wattmeter having usual current and voltage coils adapted to be connected in-and to the circuit to bemetered, an auxiliary voltage coil on said .wattmeter, a second wattmeter having usual current and volta e windin s' the current windin OfW l IlCh is 1 adapted to be connected in the circuit to be metered and the voltage winding of which to the component of the other variable which is connected in series with the auxiliary coil of the zero reading meter, and means for producinga current in said last mentioned circuit which is substantially in phase with the current of the circuit to be metered and which is of such magnitude as to reduce the reading of the zero readi'ng wattmeter to zero. n

5. Apparatus for measuring the power of low power factor alternating current circuits sub ectto varying current and voltage, comprising a senstive zero reading wattmeter having its windings connected to such a circuit in the usual way, a rugged large scale deflection watt-meter having one of its windings connected to said circuit in the usual Way and its other winding connected in series circuit relation with an auxiliary winding section of the corresponding winding of the 'se sitive wattmeter, and n'ieans for producini a current in said last mentioned circuit substantially in phase with thecurrent in the corresponding windings oi said meters which are connected to the circuit in the usual way, and of such magnitude as to reduce the read ing of the sensitive wattmeter to zero.

6. Apparatus for measuring the power of low power factor circuits comprising a zero reading wattineter having the usual current and voltage coils connected in and to the circuit to be metered, an auxiliary voltage coil included in the voltage winding of said meter, a second wattmeter having the usual ,current and voltage coils the current coil of which is adapted to be connected in series with the current coil of the first mentioned meter and the voltage coil of which is co nected in series with said auxiliary voltage 0011, a resistance 1n series wlth the current coils of said meters and an adjustable con" with the first mentioned variable regardless of variations in power factor,- and using said current together with the variable with which it is substantially in phase, to obtain a substantially unity power factor power measurement. V

in witness whereof, we have hereunto set our hands this third day of December, 1926.

GUGLIELMO (JAMILLI. ARAM BOYAJIAN. 

